Monoamine oxidase inhibition by phenelzine and brofaromine in healthy volunteers

The two monoamine oxidase (MAO) inhibitors phenelzine and brofaromine given for 2 to 3 weeks were compared in six volunteers. Blood pressure sensitivity to intravenous tyramine increased 2.6-fold during phenelzine (60 mg/day) and 4.8-fold during brofaromine, whereas sensitivity to oral tyramine increased more during phenelzine (15.7-fold vs 8.5-fold). After withdrawal of phenelzine, pressor sensitivity to oral tyramine returned to control values within 2 and for more than 8 weeks. Relative bioavailability of conjugated tyramine was elevated sixfold by brofaromine and 11.6-fold by phenelzine. Urinary elimination of tryptamine increased during phenelzine and brofaromine to 12.7-fold and threefold, respectively. 3-Methoxy-4-hydroxyphenylglycol (MHPG) and 3-methoxy-4-hydroxymandelic acid (VMA) excretion decreased during brofaromine significantly by 72% and 49%, respectively. The nonsignificant decrease of MHPG excretion and the increase of intravenous tyramine pressor sensitivity caused by phenelzine are significantly related. The data suggest that the selective reversible MAO-A inhibitor brofaromine has a larger therapeutic safety than phenelzine.